Manufacture of sodium carbonate monohydrate



June 25, 1935.

R. B. MaOMULLlN MANUFACTURE OF SODIJM CARBONATE MONOHYDRATE Filed March 25, 1952 2 Sheets-Sheet 1 'ATTORNEYS June 25, 1935. R, B MacMULLlN 2,005,868

MANUFAGTURE 0F soDIUM CARBONATE MONOHYDRATE Filed March 25", 1932 2 Sheets-Sheet 2 ATTORNEYS Patented June 25, 1935 STATES PATENT??Dwice' l* MANUFACTURE or' soDIUM oARoNATE MoNonYDaATE Robertl Burns Mac-Mullin, Niagara Falls, N. Y., assignor to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia Application March 25, 1932, Serial No. 601,144v

2 Claims.

ThisV invention relates to improvements in the vrri'sfniufacture of sodium carbonate monohydrate, Na2CO3-H2O. More particularly, the inventionv V relates to improvements in the conversion of sodium bicarbonatefNaHCOa, and sodium cari sheets of the procedures hereinafter described as operation 1 and operation 2.

-nThe conventional methods of manufacturing sodium carbonate monohydrate require, as the essential raW material, anhydrous sodium carbonate." Anhydrous sodium carbonate, or vsoda ash, is conventionally produced bymcalcination of crude ammonia soda, Ian 'operation involving substan tialexpense and tseveral difliculties. These con:- ventional' methods of manufacturing sodium carbonate monohydrate includeY hydration of anhydrous sodium. carbonate, `with a limited' propor tion of water`,at elevated temperatures, crystall lization from a 4solution-containing sodium carbonate fbyl evaporation `at temperatures above 36"- C., and` addition of anhydrous sodiumV carbonate to a solution saturated withrespect'to sodium'carbonatel at temperatures above 36 C.'

Sodium carbonate monohydrate can bepre'cipitatedirom aqueous solutions containing sodium carbonateby the addition of ammonia. `The ammoniamay be added either as a gas, as a liquid orA as an aqueous solution. By proper choice of proportions andftemperatures, high recoveries of Sodiumcarbonate monohydrate canbe obtained.'

solutionsunsaturated with respectr to these carbonates."v The addition of vamrnoniafto aqueous solutions saturatedvvith respect to sodium carb'onate` monohydrate,',NazCOaH20, also renders such solutions` unsaturated with respect to kthis carbonate initially, but,` as addition Yof ammonia' is continued', sodium :carbonate monohydrate is (Cl.I 23e-63) precipitated. This precipitation of sodium car'- bonate monohydrate, moreover, proceeds* in' the presence of other salts such as sodium' chloride and'ammonium chloride.` Insom'e cases the pres;- ence of `such other salts `may promote precipita` tion.

In carrying out the present invention`,lso`dium carbonate monohydrate Ais precipitated` `from aqueous solutions containing sodiumfcarbonate by the addition of ammonia in'proportior`1='lessy 1 than that precipitating `sodium"-carbonate." `In the application of the invention to'sodil'1m-.;bi1-l carbonate, a solution containing the'sodiumfbi carbonate is iirst converted toa solution contain*- ing sodium carbonate, advantageously by"'decom'" position with steam, for example, and theisodium carbonate monohydrate isprecipitated 'from this.l solution by the addition of ammonia. The steam for decomposition may be formed-from thesolution itself by the application vof heaty Thein-y vention is thus applicable,` for example, to Acrude sodium bicarbonate, crude ammonia lsoda for example, Without requiring the separation offso-f vdium carbonate as such. 'I f The invention will be further 'describedin connectionwithf the following example of embodiments of the invention:v f I r Example I .-Crude ammonia soda,. containing the equivalent of 133 parts of 'sodium carbonate, is-made into a'slurry with Water and this slurry` is decomposed With steam,fin theconventional manner, until approximately 8590%y `of thebi' carbonate has been converted-into thecarbon-f ate. The resulting solution'shou'ld'be .asi-cone! centrated as possiblefwithout interfering with:- the decomposition operation solutionszcontain-'f' ing l-ll'g'ram molecules of Water per rgram atomy of sodium are commonly-rproduced.'in'Jthisiman-r ner. In the absence offadded aminoni'a,,sodium sesquicarbonate is precipitatedv from this s'olu-v tion at temperatures of 30-50-C. .In-1 carrying out thisk invention.H 126 parts of ammonia-are; added to this solutionat temperatures.geitherf above. orbelovv 50 C.; at higher temperatures the addition is carried out unders1115eratmpps1.45"E

p heric pressure andat lower temperatureszcool,-l ing is'usually required.y `4 Since .thefsolubilityfof sodium carbonate monohydrate yvaries but,slight-1.`

ly with temperature, the temperature fof ysepa' tion of the precipitated sodium carbonate ml hydrate Ais not important. The vseparation'' be effected, for example, at temperatures "of 'fr 15 C. to 100 C; The yprecipitated crystall ne sodium 'carbonate K4monohydrate is separatedfrorn the mother liquor'in any-convenient manner", by"

tate sodium carbonate monohydrate.

flltering or by centrifuging. About 70% of the sodium oxide content, NazO, of the original crude ammonia soda is recovered as crystalline sodium carbonate monohydrate.

In the operation of the foregoing example, the decomposition of the original crude ammonia soda slurry should be carried out at least far enough to convert about 65% of the bicarbonate to carbonate.V An NH3-:Na ratio of '74:26 is particularly advantageous in carrying out the operation of the foregoing example. Ratios as lowy as 53:47, are useful rin carrying out the operation of the foregoing example.

In general, NHazNa ratios in the range of about 11i-3:1 arev advantageous'in carrying out the invention.

It will be understood that individual operations such as that illustrated in the foregoing example can be embodied in various composite operations -for the production of sodium carbonate. monohydrate. ularly'advantageous combined operations. These twooperations will be further described in conwiththe accompanying drawings which illustrate, as flow sheets,vthese two operations.

Operation 1.-Crude ammonia soda is dissolved in hot. water and this solution is decomposed with as described in Example I forexample. The carbon dioxideY and any ammonia recovered in this decomposition is supplied to the ammonia soda process carbonation `for the precipitationv` o1' .sodiumv bicarbonate. 'I'he carbonate. solution from the: decomposition` is cooled, to 50 C. for example, and ammoniaA gas is added to precipi- This ammonia. gasA is ac iva-ritageouslyl that recovered in .the recovery still of the ammonia soda process following thev addition of lime to the mother` liqum'.I remaining after the separation of the sodium bicarbonate, that is ammonia gas is advantageously lsubstantially free` from carbon dioxide. The crystallized sodium carbonate monohydrate is separated from the vmother liquor.

The mother liquor from which thev sodium Vcarbonate monohydrate has been separated, now poor inl sodium carbonate but rich` in ammonia, is saturated with sodium chloride, with the additim! of water ifl necessary, and. theresulting brine is carbonated;- in. the ammonia soda process, tov precipitate sodium bicarbonate. 'I'his sodium bicarbonate. is separated. lfrom the mother liquor, andthe separatedl sodium bicarbonate or part of itissupplied, dissolved: in` hot water, to the initial` decomposition. 'Carbon dioxide, with associated ammonia, recovered iny the recovery stillA o! the: ammonia. soda process priorl to the addition'rv of lime is advantageously supplied' to this carbonation,` together with anyI additional car'- bon dioxide' required.V The mother liquor.v from'v which the sodium ybicarbonategis separated'` is` supplied to the recovery still;r` Thisoperation is illustrialiedE in the flow diagramjI constituting Fig. 1y of the accompanyingdrawings. I The separated sodium carbonate monohydrate may dried in any conventional manner. If anhydrous dense sodium carbonate is the ultimate, product desired, this drying is carried out ata temperature somewhat above 100 C.,.- the sodium carbonate monohydrate thus being de hydrated to, sodium carbonate while retaining the 'pseudomorphic form of. the original sodium carbonate monohydrate crystals.

'Operation 2LCrudeammonia soda is dissolved in an. aqueous. solution of sodium carbonate. cir- I have developed two partic-` production ,of sodium bicarbmate. fdiegoarbon-v ate solution from the cooled, to 50 C. for example, and ammonia gas is added tov precipitate sodium carbonate monohydrate. The mother liquor from which the sodium carbonate monohydrate is separated is returned to theinitial decomposition, either directly or after an operation'for the recovery of ammonia from this mother liquor. If this mother liquor is returned directly to the initial decomposition, ammonia aswell as carbon dioxide will be recov- /ered in the decomposition operation.. Substantially pure carbon dioxide can be recovered in the decomposition operation, however, if this mother liquor is first stripped `of its ammonia'v content, in a recovery' still for example. mother liquor may be supplied from this recovery stillto the decomposing operationwhile VThis recovery still is advantageously heatedv indirectly, by closed steam coils for example. The ammonia recovered in this still is. advantageously used in the precipitation of sodium carbonate-,mommydrate fromthe carbonate solutionl from the decomposition operation. To maintain the-system in balance, water may be separated from the mother liquor in this recovery still and thereafter.

separated from the recovered ammonia: in any conventional manner, in a fractionatingtower for example, and discharged from the system.: This operation is illustrated in' the flowdiagram constituting Fig. 2 ofthe accompanying drawings.y

I claim:

1. In the manufacture of sodium. carbonate. monohydrate, the improvement which comprises decomposing an aqueous.: solution 'containing so-` dium bicarbonatel with steamv tol form a soltiti'osr'i containing sodium carbonate, precipitating so'- dium carbonate. monohydrate from this solution by the addition of ammoniaandseparating' the precipitatedl sodiumy carbonate monohydrate from the mother' liquor, adding sodium chloride tothe mother liquor and'carbonating the resulting brine f to precipitate sodium bicarbonate; separating the precipitated` sodium bicarbonate and supplyingy sodium bicarbonate sov precipitatedv to the first mentioned decomposition.

2. In thev manufacture of A.sodium decomposing an` aqueous solution containing socarbonate monohydrate, the improvement whichy comprises:

dium: bicarbonate with ,steam toform a solutioncontaining sodium carbonate, precipitating so dium carbonate monohydrate fromv this` solution by the addition of ammonia and'. separating the precipitated sodium carbonate rrionohydrate'fromr the mother liquor, addlng'sodium chloride to the mother liquor and carbonating the resulting brine to precipitate sodium bicarbonate, separating vtlie precipitated sodium bicarbonate and supplying.

sodium bicarbonate so precipitated` to the first-y mentioned decomposition, recovering. carbon` di,-`

oxide and ammonia from the mother liquor fromwhich sodium bicarbonate is so separated,l supplying `carbon dioxide sofrecoveredto thesaidcarbonation and supplyingv ammonia so recovered to the said precipitation ofl sodium'carbonate monohydrate. j I ROBERT BURNSTMACMULLIN. 

